1. Field of the Invention
This invention relates to polyols useful in the production of polyurethane foam. More particularly, the invention relates to rigid poloyls having a relatively low viscosity, making them particularly useful in sprayed high density foams.
2. Compounds Related to the Invention
It has long been known to prepare rigid polyurethane foams by the reaction of a polyisocyanate with a hydroxyl-terminated polyester or poly(oxyalkylene)ether having a hydroxyl number within the range of from about 350 to about 900. However, polyurethane foams prepared to data have not been entirely satisfactory for all applications. Therefore, it is necessary to design polyols and polyol systems for particular purposes. The invention herein is addressed to sprayed polyurethane foams that must be of high density.
Still further, the production of a satisfactory urethane foam requires that the relative rates of the various reactions that occur be properly balanced. This balance is normally obtained by careful selection of a catalyst system. The catalyst usually consists of a tertiary amine used alone or, when necessary, mixed with organic tin compounds in a manner well known to those skilled in the art. Supplemental amine catalysts are often used in spray foams because the foam must set quickly to perform properly.
The nitrogen-containing polyols described in U.S. Pat. Nos. 3,297,597 and 4,137,265 have overcome many of the above described problems. While these polyols have catalytic activity, usually an extraneous catalyst is necessary for the production of a sprayed, rigid foam. It was surprisingly noted that the rigid polyurethane foam prepared from these polyols is characterized by a greater ease of fire retardancy and good dimensional strength when extraneous fire retardants are employed.
In the past, the major uses of sprayed rigid urethane foam required the foam to have a density of approximately two pounds per cubic foot. However, new applications, such as roof insulation and pipe insulation, require the foam to have higher densities, on the order of 3 or 4 pcf, to give the desired compressive strength. As the foam density is increased, the fluorocarbon 11 content of the B-component decreases; thus, for a given polyol, the increase in the foam density will give a B-component with a higher viscosity.
The equipment normally used for the industrial application of sprayed urethane foam uses "double acting" positive displacement pumps which have the advantage of supplying an accurate component ratio in a continuous stream. A major disadvantage of this metering system is that it will function reliably only if the B-component has a viscosity of less than 1,000 centipoise at ambient temperature. At higher viscosities, cavitation occurs on the B-component side, resulting in a component ratio change which can affect the foam product quality.
The commercial poloy, THANOL.RTM. R-650-X, produced by Texaco Chemical Company, is widely used in spray foams because the resulting foam exhibits excellent adhesion to a variety of substrates over a wide range of temperature conditions. The product sold as THANOL R-650-X is essentially that polyol described in U.S. Pat. No. 4,137,265, incorporated by reference herein. The high viscosity of this polyol (22,000 centipoise to 37,000 centipoise at 25.degree. C.) limits its application in the higher density spray systems, because with the decrease in the fluorocarbon 11 component the overall viscosity of the B-component is too high to avoid cavitation in the equipment used for sprayed foams.